i) Field of the Invention
The present invention relates to a magnetoresistive film whose resistance changes in accordance with a magnetic field intensity, a magnetoresistive head for detecting the magnetic field intensity in accordance with the resistance change of the magnetoresistive film, an information regeneration apparatus for regenerating information recorded in a recording medium, and a magnetoresistive film manufacture method for manufacturing the magnetoresistive film.
ii) Description of Related Art
In recent years, with spread of a computer, a large amount of information has been handled in a daily manner. Such information is recorded on a recording medium by a large number of physical marks, and regenerated by an information regeneration apparatus for reading the mark on the recording medium to regenerate an electric regeneration signal.
A hard disk drive (HDD) is one of the information regeneration apparatuses, and is characterized in that a memory capacity is large and access speed to the information is fast. The HDD is provided with a magnetic disk as the recording medium whose surface is formed of a magnetic material, and a regeneration head for regenerating the information recorded on the magnetic disk. For the magnetic disk, a surface is magnetized for each micro area (one-bit region), and one bit of information is recorded in a form of a magnetization direction of the one-bit region. The regeneration head is disposed in the vicinity of the magnetic disk, and outputs an electric regeneration signal in accordance with a signal magnetic field Hsig generated from the magnetization of one-bit region of the magnetic disk to regenerate the information recorded on the magnetic disk.
At present, in many of the regeneration heads mounted on the HDD, a magnetoresistive head (MR head) including a magnetoresistive film whose resistance changes in accordance with the magnetic field from the outside is used. In the MR head, a pair of electrode terminals are disposed on La the magnetoresistive film, and during operation a sense current is passed to the magnetoresistive film from the pair of the electrode terminals. In such sense current flow state, when the MR head is relatively moved in the vicinity of the magnetic disk, an electric resistivity of the magnetoresistive film successively changes in accordance with the signal magnetic field Hsig from the magnetic disk, and a high-output regeneration signal with a voltage of a value represented by a product of the electric resistivity and the sense current value is outputted.
However, a recording density of the magnetic disk continues to be enhanced year by year, an area of one-bit region decreases with enhancement of the recording density, the signal magnetic field Hsig generated from the one-bit region is weakened, and the regeneration head for outputting a large regeneration signal is therefore necessary even for this weak signal magnetic field Hsig. As the regeneration head for outputting the large regeneration signal, a spin valve magnetoresistive head which is a magnetoresistive head utilizing a giant magnetoresistive (GMR) effect is disclosed by Japanese Patent Application Laid-Open No. 358310/1992, and practical use is starting in earnest.
The spin valve magnetoresistive head is provided with a spin valve magnetoresistive film as a multilayered film including a free magnetic layer (free layer) whose magnetization direction changes in accordance with the external magnetic field, a middle layer formed adjacent to the free layer and constituted of a nonmagnetic metal, a pinned magnetic layer (pinned layer) whose magnetization direction is fixed in a predetermined direction, and an antiferromagnetic layer formed adjacent to the pinned layer and constituted of an antiferromagnetic material for fixing the magnetization direction of the pinned layer. For the magnetoresistive film, when the external magnetic field changes, the magnetization direction of the free layer of the magnetoresistive film changes, and a resistance change is a generated in accordance with relative angle changes of the magnetization directions of the pinned layer and free layer.
Since an output of the regeneration signal of the magnetoresistive head provided with the magnetoresistive film is substantially proportional to a difference xcex94xcfx81/t between a maximum value and a minimum value of a sheet resistance changing in accordance with the external magnetic field change, with respect to the magnetoresistive effect, an ability of the magnetoresistive film is evaluated by this difference xcex94xcfx81/t in many cases. The difference xcex94xcfx81/t between the maximum value and the minimum value of the changing sheet resistance will be hereinafter referred to as resistance change xcex94xcfx81/t. Since the aforementioned spin valve magnetoresistive film has a large resistance change xcex94xcfx81/t, the high-output regeneration signal can be obtained from the magnetoresistive head provided with the magnetoresistive film.
The spin valve magnetoresistive head outputs the high-output regeneration signal in this manner, but it is demanded that a higher output be obtained by further increasing the resistance change xcex94xcfx81/t of the magnetoresistive film. As a measure for increasing the resistance change xcex94xcfx81/t, a thickness of the middle layer is reduced. When the thickness of the middle layer is too large, an excess shunt current not contributing to the magnetoresistive effect flows in the middle layer to decrease the resistance change xcex94xcfx81/t, but the decrease of the resistance change xcex94xcfx81/t is suppressed by setting the middle layer to be thin.
However, in the conventional magnetoresistive film, an interlayer coupling field Hen usually acts between the magnetization of the free layer and the magnetization of the pinned layer to set these magnetization directions to be the same direction, and with further thinning of the middle layer, the coupling field Hin increases. In the following, the coupling field Hin has a positive value when the magnetization directions are set to be the same direction, and has a negative value when the directions are set to be directions opposite to each other. By this coupling field Hin, a deviation is generated in an angle formed by the magnetization direction of the free layer and the magnetization direction of the pinned layer.
In general, the resistivity of the magnetoresistive film preferably linearly changes with respect to the change of the signal magnetic field H.,g from the magnetic disk, and to realize this linear change, it is ideal to form an angle of 90xc2x0 C. by the magnetization directions of the pinned layer and free layer in the absence of the signal magnetic field Hsig. However, when the angle deviates from 90xc2x0 by the coupling field Hin, the output voltage of the spin valve magnetoresistive head fails to linearly respond to an input of signal magnetic field Hsig, and strain of a regeneration waveform of the output voltage or another trouble occurs.
The present invention has been developed in consideration of the aforementioned situations, and an object thereof is to provide a magnetoresistive film in which increase of coupling field with thickness reduction of a middle layer is inhibited, a magnetoresistive head provided with the magnetoresistive film, an information regeneration apparatus provided with the magnetoresistive head, and a magnetoresistive film manufacture method for manufacturing the magnetoresistive film.
Among magnetoresistive films of the present invention for attaining the aforementioned object, a first magnetoresistive film is a multilayered film including: a pinned magnetic layer having magnetization whose direction is fixed; a nonmagnetic middle layer formed on the pinned magnetic layer; and a free magnetic layer formed on the middle layer and provided with magnetization whose direction changes in accordance with an external magnetic field, and indicates a magnitude of resistance in accordance with an angle formed by the magnetization direction of the pinned magnetic layer and the magnetization direction of the free magnetic layer.
A copper oxide layer of an oxide including a copper element is formed directly on the free magnetic layer, or on the free magnetic layer via an oxide layer formed of a material fabricated by oxidation of a material constituting the free magnetic layer.
Here, the copper oxide layer may be formed adjacent onto the free magnetic layer, or formed on the free magnetic layer via a predetermined layer.
Like the first magnetoresistive film of the present invention, when the copper oxide layer comprising the oxide including the copper element is formed directly on the free magnetic layer, or on the free magnetic layer via the oxide layer, as described later in an example, a value of the aforementioned coupling field Hi decreases, and the increase of the coupling field H,n accompanying the thickness reduction of the middle layer is inhibited.
In general, the resistance change of the magnetoresistive film in a magnetoresistive effect is generated by a change of a magnitude of an average free stroke in the magnetoresistive film by spin dependence scattering of a conductive electron in accordance with the external magnetic field, and the change of the magnitude of the average free stroke increases by specular reflection.
In the first magnetoresistive film of the present invention, when the copper oxide layer is formed directly on the free magnetic layer, on an interface between the free magnetic layer and the copper oxide layer, the conductive electron is specularly reflected while keeping its spin state. When the copper oxide layer is formed on the free magnetic layer via the oxide layer, the specular reflection occurs on the interface between the free magnetic layer and the oxide layer, and on the interface between the oxide layer and the copper oxide layer. Therefore, the first magnetoresistive film of the present invention indicates a large resistance change xcex94xcfx81/t by the occurrence of the specular reflection on these interfaces.
In the magnetoresistive film of the present invention, the copper oxide layer preferably has a thickness of 10 angstroms or more.
As described later in the example, when the copper oxide layer has the thickness of 10 angstroms or more, the inhibition of the increase of the coupling field Hin is effectively performed.
Moreover, when the magnetoresistive film of the present invention is provided with the oxide layer, the oxide layer preferably has a thickness of 5 angstroms or more.
For the first magnetoresistive film, since the thickness of the oxide layer is 5 angstroms or more, as described later in the example, the coupling field Hin is small, and the specular reflection of the conductive electron is satisfactorily performed on the interface between the free magnetic layer and the oxide layer.
Moreover, for the first magnetoresistive film of the present invention, a protective layer for protecting the copper oxide layer is preferably formed on the copper oxide layer.
For the first magnetoresistive film provided with the protective layer, the protective layer preferably comprises an oxide.
In the first magnetoresistive film in which the protective layer comprises the oxide, the protective layer preferably comprises Al2O3.
The copper oxide layer is physically protected, and further prevented from being oxidized or chemically protected otherwise by the protective layer.
Moreover, in the first magnetoresistive film of the present invention, the free magnetic layer preferably has a thickness of 30 angstroms or less.
For the conductive electron in the magnetoresistive film, the average free stroke by usual scattering without depending on spin is about 60 angstroms. When the thickness of the free magnetic layer is 30 angstroms or more, the conductive electron is easily scattered before specularly reflected by the interface between the free magnetic layer and the copper oxide layer, and the increase of the resistance change xcex94xcfx81/t by the specular reflection is therefore small. On the other hand, in the magnetoresistive film in which the thickness of the free magnetic layer is 30 angstroms or less, the increase of the resistance change xcex94xcfx81/t by the specular reflection is large.
Among the magnetoresistive films of the present invention for attaining the aforementioned object, a second magnetoresistive film is a multilayered film including: a pinned magnetic layer having magnetization whose direction is fixed: a nonmagnetic middle layer formed on the pinned magnetic layer; and a free magnetic layer formed on the middle layer and provided with magnetization whose direction changes in accordance with an external magnetic field, and indicates a magnitude of resistance in accordance with an angle formed by the magnetization direction of the pinned magnetic layer and the magnetization direction of the free magnetic layer.
The middle layer has a thickness of 34 angstroms or less.
A coupling layer for exerting a coupling field for directing the magnetization of the pinned magnetic layer and the magnetization of the free magnetic layer in opposite directions between the magnetizations is formed on the free magnetic layer.
For example, in the first magnetoresistive film of the present invention, the coupling layer corresponds to the copper oxide layer, or a composite layer of the copper oxide layer and oxide layer, but the coupling layer is not limited to these layers, and may be any layer as long as the coupling field for directing the magnetization of the pinned magnetic layer and the magnetization of the free magnetic layer in the opposite directions is exerted between the magnetizations.
For the magnetoresistive film heretofore put to practical use, the thickness of the middle layer is 34 angstroms or less, the coupling field Hin for directing the magnetizations in the same direction acts on the first magnetoresistive film, and the coupling field Hin increases by reducing the thickness of the middle layer. On the other hand, since the second magnetoresistive film includes the coupling layer, even with the thickness of the middle layer of 34 angstroms or less, the value of the coupling field becomes negative, and the value of the coupling field Hin can therefore be brought close to zero by reducing the thickness of the middle layer.
Among magnetoresistive heads of the present invention for attaining the aforementioned object, a first magnetoresistive head is provided with a magnetoresistive film as a multilayered film including: a pinned magnetic layer having magnetization whose direction is fixed; a nonmagnetic middle layer formed on the pinned magnetic layer: and a free magnetic layer formed on the middle layer and provided with magnetization whose direction changes in accordance with an external magnetic field, and indicating a magnitude of resistance in accordance with an angle formed by the magnetization direction of the pinned magnetic layer and the magnetization direction of the free magnetic layer. The magnetoresistive head detects the magnitude of the resistance of the magnetoresistive film to detect a strength of the external magnetic field.
A copper oxide layer of an oxide including a copper element is formed directly on the free magnetic layer, or on the free magnetic layer via an oxide layer formed of a material fabricated by oxidation of a material constituting the free magnetic layer.
In general, it is ideal to form an angle of 90xc2x0 C. by the magnetization directions of the pinned magnetic layer and free magnetic layer, for use in the magnetoresistive head, in the absence of the signal magnetic field Hsig. However, when excess magnetic fields such as the coupling field Hin exist, the angle deviates from 90xc2x0. When the angle deviates from 90xc2x0, a regeneration waveform of a regeneration signal outputted from the magnetoresistive head is strained.
Since the first magnetoresistive head employs the first magnetoresistive film of the present invention as the magnetoresistive film, and the increase of the excess coupling field Hin accompanying the decrease of the thickness of the middle layer is inhibited, the strain of the regeneration waveform is inhibited in the first magnetoresistive head.
Among magnetoresistive heads of the present invention for attaining the aforementioned object, a second magnetoresistive head is provided with a magnetoresistive film as a multilayered film including: a pinned magnetic layer having magnetization whose direction is fixed; a nonmagnetic middle layer formed on the pinned magnetic layer; and a free magnetic layer formed on the middle layer and provided with magnetization whose direction changes in accordance with an external magnetic field, and indicating a magnitude of resistance in accordance with an angle formed by the magnetization direction of the pinned magnetic layer and the magnetization direction of the free magnetic layer. The magnetoresistive head detects the magnitude of the resistance of the magnetoresistive film to detect a strength of the external magnetic field.
The middle layer has a thickness of 34 angstroms or less.
A coupling layer for exerting a coupling field for directing the magnetization of the pinned magnetic layer and the magnetization of the free magnetic layer in opposite directions between the magnetizations is formed on the free magnetic layer.
Since the second magnetoresistive head employs the second magnetoresistive film of the present invention as the magnetoresistive film, and the value of the coupling field Hin can be brought close to zero by further reducing the thickness of the middle layer, the strain of the regeneration waveform can be inhibited in the second magnetoresistive head.
Among information regeneration apparatuses of the present invention for attaining the aforementioned object, a first information regeneration apparatus is provided with a magnetic head, disposed in the vicinity of or in contact with a magnetic recording medium on which information is recorded by a magnetization direction, for detecting the magnetization direction of each point of the magnetic recording medium, and regenerates the information in accordance with the magnetization direction of each point of the magnetic recording medium detected by the magnetic head.
The magnetic head is provided with a magnetoresistive film as a multilayered film including: a pinned magnetic layer having magnetization whose direction is fixed; a nonmagnetic middle layer formed on the pinned magnetic layer; and a free magnetic layer formed on the middle layer and provided with magnetization whose direction changes in accordance with an external magnetic field, and indicating a magnitude of resistance in accordance with an angle formed by the magnetization direction of the pinned magnetic layer and the magnetization direction of the free magnetic layer. The magnetoresistive head detects the magnitude of the resistance of the magnetoresistive film to detect a strength of the external magnetic field. A copper oxide layer of an oxide including a copper element is formed directly on the free magnetic layer, or on the free magnetic layer via an oxide layer formed of a material fabricated by oxidation of a material constituting the free magnetic layer.
The first information regeneration apparatus employs the first magnetoresistive head of the present invention in the magnetic head. Similarly as the first magnetoresistive head, since the magnetic head has the strain of the regeneration waveform inhibited, the first information regeneration apparatus is high in sensitivity for detecting the magnetization direction of each point of the magnetic recording medium, and suitable for the regeneration of the information recorded with a high density on the magnetic recording medium.
Among the information regeneration apparatuses of the present invention for attaining the aforementioned object, a second information regeneration apparatus is provided with a magnetic head, disposed in the vicinity of or in contact with a magnetic recording medium on which information is recorded by a magnetization direction, for detecting the magnetization direction of each point of the magnetic recording medium, and regenerates the information in accordance with the magnetization direction of each point of the magnetic recording medium detected by the magnetic head.
The magnetic head is provided with a magnetoresistive film as a multilayered film including: a pinned magnetic layer having magnetization whose direction is fixed; a nonmagnetic middle layer formed on the pinned magnetic layer; and a free magnetic layer formed on the middle layer and provided with magnetization whose direction changes in accordance with an external magnetic field, and indicating a magnitude of resistance in accordance with an angle formed by the magnetization direction of the pinned magnetic layer and the magnetization direction of the free magnetic layer. The magnetoresistive head detects the magnitude of the resistance of the magnetoresistive film to detect a strength of the external magnetic field.
The middle layer has a thickness of 34 angstroms or less.
A coupling layer for exerting a coupling field for directing the magnetization of the pinned magnetic layer and the magnetization of the free magnetic layer in opposite directions between the magnetizations is formed on the free magnetic layer.
The second information regeneration apparatus employs the second magnetoresistive head of the present invention in the magnetic head. Similarly as the second magnetoresistive head, in the magnetic head, since the strain of the regeneration waveform is inhibited, the second information regeneration apparatus is high in sensitivity for detecting the magnetization direction of each point of the magnetic recording medium, and suitable for the regeneration of the information recorded with a high density on the magnetic recording medium.
Among magnetoresistive film manufacture methods of the present invention for attaining the aforementioned object, there is provided a first magnetoresistive film manufacture method for manufacturing a magnetoresistive film as a multilayered film including: a pinned magnetic layer having magnetization whose direction is fixed; a nonmagnetic middle layer formed on the pinned magnetic layer; and a free magnetic layer formed on the middle layer and provided with magnetization whose direction changes in accordance with an external magnetic field, and indicating a magnitude of resistance in accordance with an angle formed by the magnetization direction of the pinned magnetic layer and the magnetization direction of the free magnetic layer.
The method includes: a free magnetic material layer lamination step of laminating the middle layer, and subsequently laminating a free magnetic material layer including a material constituting the free magnetic layer on the middle layer;
a metal layer lamination step of laminating a metal layer including a metal on the free magnetic material layer laminated in the free magnetic material layer lamination step; and
a plasma oxidation step of exposing the metal layer laminated by the metal layer lamination step to oxygen in a plasma state to oxidize the metal layer.
In the magnetoresistive film finally formed through these respective steps, the free magnetic material layer itself, or a partial layer of a thickness direction in the free magnetic material layer constitutes the free magnetic layer.
According to the first magnetoresistive film manufacture method, as described later in the example, by oxidation of the metal layer laminated on the free magnetic material layer in the plasma oxidation step, the magnetoresistive film is manufactured in which the coupling field Hin is reduced and the increase of the coupling field Hin accompanying the thickness reduction of the middle layer is inhibited.
In the first magnetoresistive film manufacture method of the present invention, the plasma oxidation step preferably includes a step of oxidizing the metal layer, and a part of the free magnetic material layer on the side of the metal layer.
In a conventional art, an oxide film is sometimes formed on the free magnetic layer by natural oxidation, but it is difficult to form the oxide film with a controlled desired thickness depending on the natural oxidation. Moreover, although the oxide film can be formed directly on the free magnetic layer by performing plasma oxidation, in the direct plasma oxidation, by excessively strong oxidation, it is still difficult to form the oxide film with the controlled desired thickness.
On the other hand, since the first magnetoresistive manufacture method comprises forming the metal layer on the free magnetic material layer comprising the material constituting the free magnetic layer, and oxidizing a part of the free magnetic material layer through the metal layer by the plasma oxidation step, during formation, the oxide layer fabricated by oxidation of the free magnetic material layer can be controlled to provide the desired thickness. Moreover, by forming the oxide layer whose thickness is controlled, the coupling field Hin can be controlled.
Furthermore, in the first magnetoresistive film manufacture method of the present invention, the metal layer laminated in the metal layer lamination step preferably includes copper or a copper alloy.
In this metal layer of copper or the copper alloy, control of the coupling field Hin is effectively performed.
Moreover, in the first magnetoresistive film manufacture method, the plasma oxidation step is preferably performed simultaneously with lamination of a new layer on the metal layer.
In the first magnetoresistive film manufacture method including the lamination of the new layer, the new layer preferably comprises the oxide.
In the first magnetoresistive film manufacture method including the lamination of the new layer comprising the oxide, the new layer may comprise Al2O3.
By laminating the oxide, and the like on the metal layer by sputtering or the like in this manner, for example, the new layer having a function of protecting the metal layer is formed, and additionally the metal layer can be oxidized.
In the first magnetoresistive film manufacture method of the present invention, the plasma oxidation step is preferably performed in an atmosphere including at least one of Ar and oxygen.
When the plasma oxidation step includes, for example, a step of laminating the new layer comprising the oxide onto the metal layer by sputtering or the like, even with the sputtering performed in the atmosphere including Ar but including no oxygen, the metal layer is plasma-oxidized.
Moreover, when the plasma oxidation step does not include the step of lamination of the new layer, the atmosphere including oxygen is used to perform the plasma oxidation.
Furthermore, in the atmosphere of mixture of Ar and oxygen, the thickness of the oxide layer can be controlled by change of a mixture ratio, and the like.
Additionally, even when the plasma oxidation step is performed simultaneously with the lamination of the oxide, by performing the step in the atmosphere including oxygen, the coupling field Hin of the magnetoresistive film manufactured by the first magnetoresistive film manufacture method tends to be reduced.
In the first magnetoresistive film manufacture method of the present invention, in the metal layer lamination step, the metal layer is preferably formed in a thickness of 10 angstroms or more.
In the magnetoresistive film manufactured by forming the metal layer in the thickness of 10 angstroms or more, as described later in the example, the reduction of the coupling field Hin can effectively be performed.
Moreover, in the first magnetoresistive film manufacture method of the present invention, in the plasma oxidation step, the free magnetic material layer is preferably oxidized to a depth of 5 angstroms or more in a thickness direction from a metal layer side.
When the free magnetic material layer is oxidized to the depth of 5 angstroms or more, as described later in the example, the coupling field Hin is small, and the specular reflection of the conductive electron is satisfactorily performed on an interface of the free magnetic material layer between an oxidized portion and a non-oxidized remaining portion.
Moreover, in the first magnetoresistive film manufacture method of the present invention, for the entire thickness of the free magnetic material layer, the thickness of the portion which has not been oxidized in the plasma oxidation step is preferably 30 angstroms or less.
As described above, in the magnetoresistive film in which for the thickness of the free magnetic layer, that is, the entire thickness of the free magnetic material layer, the thickness of the non-oxidized portion is 30 angstroms or less, the specular reflection of the conductive electron on the interface of the free magnetic material layer between the oxidized portion and the non-oxidized remaining portion largely contributes to the increase of the resistance change xcex94xcfx81/t.
Among the magnetoresistive film manufacture methods of the present invention for attaining the aforementioned object, there is provided a second magnetoresistive film manufacture method for manufacturing a magnetoresistive film as a multilayered film including: a pinned magnetic layer having magnetization whose direction is fixed; a nonmagnetic middle layer formed on the pinned magnetic layer; and a free magnetic layer formed on the middle layer and provided with magnetization whose direction changes in accordance with an external magnetic field, and indicating a magnitude of resistance in accordance with an angle formed by the magnetization direction of the pinned magnetic layer and the magnetization direction of the free magnetic layer.
The method includes: a free magnetic material layer lamination step of laminating a free magnetic material layer comprising a material constituting the free magnetic layer on the middle layer;
an oxidation control layer lamination step of laminating a predetermined oxidation control layer on the free magnetic material layer laminated in the free magnetic material layer lamination step; and
a plasma oxidation step of exposing the oxidation control layer laminated by the oxidation control layer lamination step to oxygen in a plasma state to oxidize the free magnetic material layer to a predetermined depth in a thickness direction from an oxidation control layer side through the oxidation control layer.
The oxidation control layer corresponds, for example, to the metal layer laminated in the metal layer lamination step in the first magnetoresistive film manufacture method of the present invention, but this is not limited, and any layer may be used as long as the free magnetic material layer is oxidized to the predetermined depth in the thickness direction from the oxidation control layer side through the oxidation control layer by exposure to oxygen in the plasma state. In the second magnetoresistive film manufacture method, since the oxidized thickness of the free magnetic material layer is controlled by the oxidation control layer, the magnetoresistive film controlled to have a small coupling field Hin is manufactured.